US20070060977A1 - Implantable medical device communication system with macro and micro sampling intervals - Google Patents

Abstract

A communication signal is communicated between an implantable medical device including an implant transceiver and an external unit including an external unit transceiver. At least one of the transceivers includes a receiver capable of sampling a communication channel for the communication signal at times based on a macro sampling interval and a micro sampling interval. The sampling includes a series of micro samples. The duration of the series of micro samples is less than the macro sampling interval.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)
• Reference is made to the following applications, filed concurrently herewith: [Attorney Docket No. P22283] “SYSTEM AND METHOD FOR UNSCHEDULED WIRELESS COMMUNICATION WITH A MEDICAL DEVICE,” by Gregory J. Haubrich, Len D. Twetan; David Peichel; Charles H. Dudding; George C. Rosar; and Quentin S. Denzene, [Attorney Docket No. P20607] “SYSTEM AND METHOD FOR UNSCHEDULED WIRELESS COMMUNICATION WITH A MEDICAL DEVICE,” by Quentin S. Denzene and George C. Rosar, and [Attorney Docket No. P23271] COMMUNICATION SYSTEM AND METHOD WITH PREAMBLE ENCODING FOR AN IMPLANTABLE MEDICAL DEVICE,” by Gregory J. Haubrich, Javaid Masoud, George C. Rosar, Glenn Spital, Quentin S. Denzene, incorporated herein by reference in their entireties.
FIELD OF THE INVENTION
• The present invention relates implantable medical devices, and more particularly, to wireless communication with implantable medical devices.
BACKGROUND OF THE INVENTION
• Implantable medical devices (IMDs) provide therapies and monitor a wide variety of physiological events. With the increased uses of IMDs has also come the need for improved methods of communicating with and between IMDs.
• Conventionally, communication with IMDs has been with magnetic field communication systems. Such systems, however, are generally only capable of communicating over very short distances, on the order of a few inches. As a result, a magnetic head of a programmer (or other external device) needs to be placed near to the IMD for communication to occur. More recently, radio frequency (RF) based communication systems have been developed for use with IMDs. RF communication provides a number of benefits over magnetic field communication systems, including much greater communication distances. However, conventional RF communication systems consume more battery power than magnetic field communication systems, thus impacting the service life of the IMD battery.
• Accordingly, there is a need to improve RF receiver efficiency and inter-IMD communication modalities to conserve battery life.
• RF communication may generally be divided into two categories: synchronous and asynchronous. Synchronous communication is conducted at scheduled times. However, in synchronous communication systems, the internal clocks of two communicating devices are prone to drift over time. As more time elapses, the internal clocks become increasingly out of sync, such that neither device can precisely detect when the other device will commence communication. To compensate for this drift, one or both of the devices must stay in an “on” mode. During that time, energy is consumed while no communication is effected.
• In an asynchronous communication system, transmission occurs at random times. Because it is impractical to maintain the receiver on at all times, asynchronous communication systems utilize sampling methods in which the receiver is repeatedly turned on for brief periods to check for a transmission signal and turned on fully when the signal is detected. The more often the receiver is turned on, the faster the response time of the receiver. However, more energy is required. To guarantee that data will be received, the transmitter transmits a preamble for at least as long as the time interval between samples prior to transmitting a message. Once the preamble is detected, the receiver remains on until the message is received. As a result, energy is consumed by the receiver while receiving the preamble, a time in which no valuable communication is taking place.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic diagram illustrating bi-directional RF communication between an implantable medical device (IMD) and an external unit.
• FIG. 2 is a block diagram illustrating the components of an IMD and the external unit that make up an RF communication system.
• FIG. 3 is a time line illustrating a transmission bit stream from a transmitter of the external unit and receiver on-times of the IMD.
• FIG. 4 is a flow chart illustrating one embodiment of a method of operating the transmitter of the external unit.
• FIG. 5 is a flow chart illustrating one embodiment of the method of operating the receiver of the IMD.
• FIG. 6 is a time line illustrating a transmission bit stream from a transmitter of the IMD and receiver on-times of the external unit.
• FIG. 7 is a flow chart illustrating one embodiment of a method of operating the transmitter of the IMD.
• FIG. 8 is a flow chart illustrating one embodiment of a method of operating the receiver of the external unit.
DETAILED DESCRIPTION
• According to an embodiment of the present invention, a communication system includes an implantable medical device having a first transceiver and an external unit including a second transceiver. At least one of the transceivers includes a receiver configured to sample a communication channel based on a macro sampling interval and a micro sampling interval. The duration of a series of micro samples is spaced by the micro sampling interval and is set to be smaller than the macro sampling interval.
• FIG. 1 is a schematic diagram illustrating communication system10 for communication betweenIMD12, which includeslead14 andantenna16, andexternal unit18. In one embodiment, IMD12 is an implantable cardioverter defibrillator (ICD). However, the present invention is broadly applicable to many types of medical devices, including implantable and externally mounted medical devices. IMD12 includes features to sense, detect, and monitor cardiac signals from patient P and delivers them as needed.Lead14 is implanted to transfer information as well as provide therapy to specific chambers of the heart.Antenna16 is used to communicate withexternal unit18 and may be any device capable of sending or receiving electromagnetic waves, including for example a surface mounted antenna, an inductor, or a half-wave strip.
• External unit18 is a device, such as a programmer, capable of bi-directional communication with IMD12 viaantenna20.External unit18 includesantenna20, which may be any type of RF antenna capable of communicating in the desired RF frequencies withIMD12, and may be located inside or outside of a housing ofexternal unit18.
• FIG. 2 is a block diagram illustrating some of the functional components ofIMD12 andexternal unit18 that make up communication system10.External unit18 includesantenna20, circuit27, andtransceiver28.Antenna20 is coupled totransceiver28. Circuit27 includes a microcomputer and that controls the operation ofexternal unit18.Transceiver28 allows external unit circuitry27 to transmit and receive communications withIMD12.Transceiver28 includestransmitter32 andreceiver34, which are coupled toantenna20.
• IMD12 includesantenna16,IMD circuitry29, and transceiver30 (which includestransmitter36 and receiver38).IMD circuitry29 includes a microprocessor for controlling the operation ofIMD12 and for processing medical data, therapy delivery circuitry for delivering a therapy throughlead14, and sensors for generating medical data relating to patient P (including data generated by detecting electrical signals on lead14). Transceiver30, andantenna16 enableIMD circuitry29 to transmit and receive communications withexternal unit18.
• Communication between IMD12 andexternal unit18 can be performed over any communication band, such as a public radio frequency band, or the Medical Implant Communication (MICs) band between 402 MHz and 405 MHz. Although the present invention is described with reference to radio frequency bands, it is recognized that the present invention is also beneficial with other types of electromagnetic communication.
• Because IMD12 has a finite battery capacity, an important consideration in the design ofRF communication system26 is the energy efficiency ofIMD12. A substantial factor in the energy efficiency ofIMD12 is the time transceiver30 spends either transmitting or receiving. By decreasing the total on-time of transceiver30, the energy efficiency of transceiver30 is improved, leading to increased battery life ofIMD12. Energy efficiency is less of an issue in the design oftransceiver28 ofexternal unit18, becauseexternal unit18 is generally connected to an external power source such as a 120V AC. Therefore, methods ofoperating transceivers28 and30 that reduce the energy consumption of transceiver30, even in exchange for additional energy consumption oftransceiver28, are beneficial.
• While transmitters only need to be turned on when there is something to transmit, receivers must be turned on much more frequently. No communication can take place unless the receiver is on, at least momentarily, to detect an attempted transmission. To provide a fast response time, a receiver may sample a communication channel as often as twice every second or more. A receiver that turns on twice every second will turn on 172,800 times in one day. A transmitter, on the other hand, may turn on only a handful of times in that same period. Therefore, increased energy efficiency of a receiver can provide a substantial increase in the effective life of the device.
• The present invention utilizes macro and micro sampling intervals to improve the energy efficiency of the transceivers of a communication system. Two examples will now be described with reference toFIGS. 3-5 and6-8 respectively. In the first example,transmitter32 ofexternal unit18 transmits toreceiver38 ofIMD12.Receiver38 operates by sampling at macro sampling intervals to detect apreamble segment42, followed by sampling at micro sampling intervals to detectattention segment44, and thereafter receivedata48. This reduces the energy consumed byreceiver38 ofIMD12. The second example reverses the roles such thattransmitter36 ofIMD12 transmits toreceiver34 ofexternal unit18.Receiver34 operates by calculating a drift window surrounding a scheduled time slot. Scheduled time slots are spaced by the macro sampling interval.Receiver38 samples at each micro sampling interval within the drift window until it detectsattention segment94 and thereafter receivesdata98.
• Sampling based on macro sampling intervals and micro sampling intervals decreases the total on-time ofreceiver34 or38 and correspondingly reduces the total energy consumed. The energy savings are realized as a result ofreceiver34 or38 being turned off between samples, rather than staying on during each of the sampling intervals.
• FIGS. 3-5 illustrate a method for transmitting data fromexternal unit18 toIMD12.FIG. 3 is a timeline illustrating transmission bit stream41 fromexternal unit transmitter32 and receiver on-times49 ofIMD receiver38.Transmission bit stream41 includespreamble segment42, attention (ATTN)segment44,frame sync segment46, anddata48.
• Preamble segment42 is a portion oftransmission bit stream41 having a recognizable pattern.Attention segment44 is a transmission bit stream also having a recognizable pattern, but one that is distinct frompreamble segment42.Frame sync segment46 is a brief pattern of bits that immediately precedesdata48 and is distinguishable fromattention segment44 anddata48.Data48 followsframe sync segment46 and includes whatever data is to be transmitted fromexternal unit18 toIMD12.
• For example,preamble segment42 may be a transmission of alternating on-off keyed (OOK) 0 and 1 bits, each having a duration of about 50 microseconds, resulting in an about 10 kHz transmission.Attention segment44 may be a transmission of alternatingOOK 1 and 0 bits, each having a duration of 50 microseconds. This transmission is equivalent topreamble segment42 with a 180 degree phase shift. In one embodiment,frame sync segment46 is an OOK transmission of eight 1 bits. A pattern of a known length, such as eight bits is beneficial to ensure thatframe sync segment46 is not confused withdata48.
• IMD receiver on-times49 are also illustrated inFIG. 3, which includemacro samples50,micro samples52, attention detectperiod54, frame sync detectperiod56, and receivedata period58. Receiver on-times49 are periods in whichreceiver38 is turned on either to sample for or receivetransmission bit stream41. Between receiver on-times49,receiver38 is turned off to conserve energy. Receiver on-times49 will be described in further detail below with reference toFIGS. 4 and 5.
• FIG. 4 is a flow chart illustrating one embodiment of a method of operatingtransmitter32 ofexternal unit18. The method includes calculating a drift window (step60), waiting until time to begin transmission (step61), transmitting preamble segment (step62), transmitting attention segment (step64), transmitting frame sync segment (step66), and transmitting data (step68). In this embodiment,transmitter32 operates in a synchronous communication mode in which bothIMD12 andexternal unit18 both recognize a scheduled time slot for communication. However, over time the internal clocks may slowly drift away from each other, such that the exact scheduled time slot is no longer equivalent between the two devices.
• To account for the possible drift betweenIMD12 andexternal unit18,transmitter32 calculates a drift window (step60). The deviation between the scheduled time slot according to the external unit's clock, and the scheduled time slot according to the clock ofIMD12 gives rise to the concept of a drift window. The drift window is the time interval, according to one device's clock, that encompasses the potential deviation in the scheduled time slots according to the other device's clock.
• For example, if the maximum drift is known to be 100 parts per million (ppm), and it has been one hour since the last communication, the drift window is calculated bytransmitter32 to be about 0.36 seconds. ((3600 seconds/hour)×(100/1,000,000)=0.36 seconds/hour.) With the drift window known,transmitter32 can determine the earliest time in whichreceiver38 would expect communication to begin, and begin communication at that time (step61). Specifically, the time to begin communication is calculated bytransmitter32 as the scheduled time slot (according to the external unit clock), minus ½ of the drift window period.
• When it is time to transmit (step61),transmitter32 transmits preamble segment42 (step62).Preamble segment42 informsreceiver38 thattransmitter32 has begun the transmission process. In one embodiment,preamble segment42 is transmitted for a period equal to or greater than the length of the drift window. By transmittingpreamble segment42 for a period at least as long as the drift window,transmitter32 ensures thatreceiver38 will turn on and begin receiving at some time duringpreamble segment42.
• Afterpreamble segment42 has been transmitted (step62),transmitter32 transmits attention segment44 (step64).Attention segment44 informsreceiver38 that data transmission is about to begin. In one embodiment,attention segment44 is transmitted for a period of at least the micro sampling interval ofreceiver38. The micro sampling interval is the period of time between consecutivemicro samples52. The micro sampling interval, for example, is 0.1 seconds. By transmittingattention segment44 for a duration equal to or greater than, the micro sampling interval ofreceiver38,transmitter32 ensures thatreceiver38 will turn on during, and receive a portion of,attention segment44.
• Afterattention segment44 has been transmitted (step64),frame sync segment46 is transmitted (step66).Frame sync segment46 informsreceiver38 that data transmission immediately follows, and serves to allowreceiver48 to determine exactly when data begins. In one embodiment,frame sync segment46 consists of a fixed length. In thisway receiver38 can distinguish betweenframe sync segment46 anddata48 even if the pattern indata48 continues the same pattern offrame sync segment46. Immediately following the transmission of frame sync segment46 (step66),data48 is transmitted (step68), which includes whatever data is to be transmitted fromexternal unit18 toIMD12, such as instructions, requests for information, pure data, transmitter ID, intended receiver ID, packet size, cyclic redundancy code (CRC), or any other desired codes or information.Data48 can also be encrypted for greater security. At the end ofdata48, an end of transmission code may also be included that informsreceiver38 that the transmission of data (step68) is complete. Following the transmission of data48 (step68),transmitter32 waits until the next scheduled communication time (steps60 and61).
• Becausetransmitter32 knows the transmission time ofpreamble segment42,attention segment44,frame sync segment46, anddata48,transmitter32 also knows exactly how long the total transmission will take.Transmitter32 can provide this information to a user who initiated the telemetry transaction betweenexternal unit18 andIMD12 to inform the user of the status of the communication.
• FIG. 5 is a flow chart illustrating operation ofreceiver38 ofIMD12. The method includes macro sampling to detect preamble segment42 (step70) at macro sampling interval (step72), micro sampling to detect attention segment44 (step74) at micro sampling intervals (step76) untilattention segment44 is detected, maintainingreceiver38 on until detection of frame sync segment46 (step78), and receiving data48 (step80).
• Receiver38 begins by macro sampling forpreamble segment42 at the scheduled time slot (step70). Between each macro sample, ifpreamble segment42 is not detected,receiver38 turns off for a macro sampling interval (step72), which is equal to the time between scheduled communication time slots. It is beneficial forreceiver38 to sample for only a short duration to conserve energy. In one embodiment,receiver32 is turned on for 2 milliseconds per sample. Ifreceiver38 detectspreamble segment42 while macro sampling,receiver38 knows thattransmitter32 has begun the transmission oftransmission bit stream41.
• Afterreceiver38 has detectedpreamble segment70, the process of micro sampling to detectattention segment42 begins (step74).Receiver38 turns off between consecutive micro samples for a micro sampling interval (step76) to further conserve energy. As the names suggest, the micro sampling interval is less than the macro sampling interval. Furthermore, the duration of a series of micro samples is also less than the macro sampling interval. During each micro sample,receiver38 verifies thattransmission bit stream41 is still present, and also monitors forattention segment44 to begin.
• By turning offreceiver38 between micro samples, considerable energy savings can be realized. For example, 98% of the energy is conserved betweenmacro sample50 and detection ofattention segment54, if eachmicro sample52 lasts for 2 milliseconds, and the micro sampling interval is 0.1 seconds, as compared to maintainingreceiver38 on during this same period.
• Micro sampling (step74) continues untilattention segment44 is detected. At this point,receiver38 knows thattransmitter32 is about to begin transmittingdata48. As a result,receiver38 stays on and continues receiving the rest of attention segment44 (Step78) to detectframe sync segment46. After receiving frame sync segment46 (step78),receiver38 receives data48 (step80) that immediately follows.Receiver38 then waits until the next scheduled time slot (step72) to macro sample for transmission bit stream41 (step70).
• Although the embodiment ofFIGS. 3-5 has been described with reference to a synchronous communication system, it is recognized that it is equally applicable to an asynchronous communication system. In such a case,transmitter32 does not know whenreceiver38 will sample for a transmission, but it does know that it will occur within the macro sampling interval. By transmittingpreamble42 to a duration at least as long as the macro sampling interval,transmitter32 is able to guarantee that the transmission will be received byreceiver38.
• FIGS. 6-8 illustrate a system and method for transmitting data fromIMD12 toexternal unit18 in a synchronous communication system. The system and method reduces the energy consumed bytransmitter36 ofIMD12, and provides an energy efficient method of operatingreceiver34.
• FIG. 6 is a timeline illustrating transmission bit stream92 fromtransmitter36 ofIMD12 and receiver on-times100 ofreceiver34 ofexternal unit18. Transmission bit stream92 includesattention segment94,frame sync segment96, anddata98.
• Attention segment94 is a transmission bit stream having a repeating and recognizable pattern. In one embodiment,attention segment94 is a transmission of alternating on-off keyed (OOK) 1 and 0 bits each having a duration of 50 microseconds, resulting in a 10 kHz transmission. Any other recognizable pattern could be used.
• Frame sync segment96 is a brief pattern of bits distinguishable fromattention segment94 anddata98 that immediately precedesdata98. In one embodiment,frame sync segment96 is an OOK transmission of eight 1 bits. Any other pattern of bits could be used, as long asreceiver34 can distinguish it from bothattention segment94 anddata98. A pattern of a known length, such as eight bits, is beneficial to ensure thatframe sync segment96 is not confused withdata98.Data98 followsframe sync segment96 and includes whatever data is to be transmitted fromIMD12 toexternal unit18.
• Receiver on-times100, as illustrated inFIG. 6, includemicro samples102, attention detectperiod104, frame sync detectperiod106, and receivedata period108. Receiver on-times100 are periods whenreceiver34 is turned on to sample for or receive transmission bit stream92. Between receiver on-times100,receiver34 is turned off to conserve energy. Receiver on-times100 will be described in further detail below with reference toFIGS. 7 and 8.
• FIG. 7 is a flow chart illustrating one embodiment of a method of operatingtransmitter36 ofIMD18. The method includes waiting for data to transmit (step110) at a scheduled time that occurs at the macro sampling internal (step111), transmitting attention segment (step112), transmitting frame sync segment (step114), and transmitting data (step116). To conserve energy withinIMD12,transmitter36 is preferably kept off as much as possible.
• If there is data that needs to be transmitted,transmitter36 begins transmission bit stream92 at a time in whichIMD12 andexternal unit18 have a scheduled communication session time slot. If data is available to transmit (step110) at the macro sampling interval (step111),transmitter36 transmits attention segment94 (step112) with a duration that slightly exceeds the micro sampling interval.Attention segment94 serves to informreceiver34 thattransmitter36 is about to transmit data. As described below,receiver34 performs a series ofmicro samples102 to detect the presence of transmission bit stream92. Eachmicro sample102 is spaced by the micro sampling interval. In one embodiment, the micro sampling interval is 0.1 seconds. By transmittingattention segment94 for a period equal to the micro sampling interval ofreceiver34,transmitter36 ensures thatreceiver34 will turn on during, and receive a portion of,attention segment94.
• Afterattention segment94 has been transmitted (step112),frame sync segment96 is transmitted (step114).Frame sync segment96 informsreceiver34 that data transmission immediately follows so thatreceiver34 can determine exactly whendata98 begins. In one embodiment,frame sync segment96 consists of a fixed length. In thisway receiver34 can distinguish betweenframe sync segment96 anddata98 even if the pattern indata98 continues the same pattern offrame sync segment96.
• Immediately following the transmission of frame sync segment96 (step114),data98 is transmitted (step116).Data98 includes whatever data is to be transmitted fromIMD12 toexternal unit18, and may include instructions, requests for information, pure data, transmitter ID, intended receiver ID, packet size, cyclic redundancy code (CRC), or any other desired codes or information.Data98 can be encrypted for greater security.Data98 may also include an end of transmission code that informsreceiver34 that the transmission of data (step116) is complete. Following the transmission of data98 (step116),transmitter36 waits for more data to transmit (step110) at the next scheduled communication time (step111).
• The method of operatingtransmitter36 ofFIG. 7 is beneficial in reducing the energy consumed bytransmitter36 ofIMD18 by reducing the transmitter on-time needed to transmitdata98. This method also reduces the energy consumed bytransmitter36 by shifting the burden of compensating for potential drift fromIMD transmitter36 toexternal unit receiver34. Rather than transmitting preamble42 (shown inFIG. 3) throughout the drift window period,receiver34 ofexternal unit18 samples periodically throughoutdrift window103. Although this may slightly increase the energy consumed byreceiver34, it greatly reduces the energy consumed bytransmitter36. Because it is generally much easier to change the battery ofexternal device18 than the battery ofIMD12, the increased efficiency oftransmitter36 ofIMD12 is worth the slight increase in energy consumed byreceiver34 ofexternal unit18.
• In addition, as wireless communication devices become more common, problems associated with collisions (two or more transmissions occurring at the same time on the same communication channel) also grow. Therefore, this method of operatingtransmitter36 is beneficial in reducing the risk of collisions by reducing the total transmission time oftransmitter36.
• FIG. 8 is a flow chart illustrating a method of operatingreceiver34 ofexternal unit18. The method includes calculating drift window103 (step120), waiting for the time to begin transmission (step122),micro sampling102 during the drift window to detect attention segment94 (step124), waiting for a micro sampling interval between micro samples (step126), maintainingreceiver34 on to detect frame sync segment96 (step128), and receiving data98 (step130).
• Receiver34 begins by calculating the drift window (step120). The drift window calculation enablesreceiver34 to know the time period in which transmission bit stream92 could occur. Although communication is scheduled for a certain time, the actual time of communication often varies due to drift between the internal clocks ofIMD12 andexternal unit18. As a result,receiver18 is operated to monitor duringdrift window103 to detect whentransmitter36 begins communication. The drift window is calculated by multiplying the time that has elapsed since the last synchronization by the maximum drift per unit of time. For example, if the maximum drift is known to be 100 ppm, and it has been one and a half hours since the last communication, the drift window would be about 0.54 seconds. ((3600 seconds/hour)×1.5 hours×(100/1,000,000)=0.54 seconds.)FIG. 6 illustrates an example ofdrift window103 having a duration of about 0.6 seconds.
• After calculation of the drift window (step120),receiver34 waits until the appropriate time to begin monitoring. In order to be sure thatreceiver34 does not miss transmission bit stream92,receiver34 must begin monitoring at the beginning of the drift window. This beginning time is calculated byreceiver34 by subtracting ½ of the duration of the drift window, described above, from the scheduled time slot (according to the clock of receiver34), which occurs at a macro sampling interval after the previous scheduled time slot. By beginning to monitor at this time, and continuing to monitor throughout the duration ofdrift window103,receiver34 ensures that it will be sampling at some time duringattention segment94 of transmission bit stream92.
• Once the time to begin monitoring has arrived (step122),receiver34 begins micro sampling to detect attention segment94 (step124).Receiver34 micro samples the communication channel after each micro sampling interval of the drift window. It is beneficial to reduce the amount of on-time ofmicro samples102, because the shorter they are, the less energy is used to take the sample. In one embodiment, eachmicro sample102 is 2 milliseconds long. After eachmicro sample102,receiver34 turns off for a micro sampling interval (step126), such as 0.1 seconds, until the nextmicro sample102.Micro sampling intervals126 allowreceiver34 to save additional energy while waiting for data transmission to begin.
• Afterreceiver34 has detectedattention segment94 of transmission bit stream92 (step124),receiver34 knows thattransmitter36 is about to begin transmittingdata98. As a result,receiver34 stays on untilframe sync96 is detected (step128).
• Immediately after the reception offrame sync96,data98 is received by receiver34 (step130).Receiver34 then waits until the next time to begin monitoring (steps120 and122), which occurs after about a macro sampling interval.
• The method of operatingreceiver34 reduces the energy consumed bytransmitter36 ofIMD12 by reducing the amount of time thattransmitter36 must be on.
• Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. In particular, the present invention has been described with reference to implantable medical devices and external units. It is recognized that in some situations it would be desirable to use the present invention for communications between implantable medical devices, between external units, among a wireless network of implantable and external devices, or to reverse the roles of the implantable medical device and the external unit.

Claims (28)

1. A medical device comprising:

device circuitry for controlling the operation of the device and for processing data; and

a receiver for sampling energy on a communication channel based on a macro sampling interval and a micro sampling interval, a duration of a series of samples, spaced by the micro sampling interval, being less than the macro sampling interval, the receiver sampling to detect presence of a transmission signal on the communication channel, and to thereafter receive data contained in the transmission signal.

2. The medical device ofclaim 1, wherein the receiver first samples to detect the presence of a preamble segment of the transmission signal, and subsequently samples to detect presence of an attention segment of the transmission signal.

3. The medical device ofclaim 2, wherein the receiver remains on after detecting presence of the attention segment to receive a frame sync segment and the data.

4. The medical device ofclaim 2, wherein a duration of the preamble segment is greater than the macro sampling interval.

5. The medical device ofclaim 2, wherein a duration of the attention segment is greater than the micro sampling interval.

6. The medical device ofclaim 1, wherein the receiver samples to detect the transmission signal, and once the transmission signal has been detected the receiver remains on to receive the data.

7. The medical device ofclaim 6, wherein the receiver samples within a drift window of a scheduled time slot.

8. The medical device ofclaim 7, wherein the time between the scheduled time slot and a next scheduled time slot is equal to the macro sampling interval.

9. The medical device ofclaim 6, wherein the receiver samples to detect the attention segment of the transmission signal.

10. The medical device ofclaim 9, wherein the micro sampling interval of the receiver exceeds a duration of the attention segment.

11. The medical device ofclaim 9, wherein the receiver remains on after detecting an attention segment until a frame sync segment and the data have been received.

12. The medical device ofclaim 1, wherein the medical device is an implantable medical device.

13. A method of operating a receiver of a medical device, the method comprising:

sampling at a first time to determine whether energy is present on a communication channel, the first time based on a macro sampling interval;

sampling at periodic times after the first time with a series of samples to determine if data is about to be transmitted, the periodic times based on a micro sampling interval, wherein a duration of the series of samples is less than the macro sampling interval; and

turning on to receive the data after determining that data is about to be transmitted.

14. The method ofclaim 13, wherein the first time is a scheduled time slot.

15. The method ofclaim 13, wherein the receiver samples with the series of samples only if energy is detected at the first time.

16. The method ofclaim 13, wherein sampling at the first time comprises sampling for a preamble segment of a transmission signal.

17. The method ofclaim 16, wherein a duration of the preamble segment is greater than the macro sampling interval.

18. The method ofclaim 13, wherein sampling with a series of samples comprises sampling for an attention segment.

19. The method ofclaim 18, wherein a duration of the attention segment is greater than the micro sampling interval.

20. The method ofclaim 13, wherein the receiver samples with the series of samples, even if energy is not detected at the first time, and wherein the duration of the series of samples being greater than a drift window of a scheduled time slot.

21. The method ofclaim 20, wherein the receiver calculates the beginning of the drift window by calculating a duration of the drift window based upon a length of time since a previous communication and subtracting one half of the duration of the drift window from a scheduled time slot.

22. The method ofclaim 13, wherein the medical device is an external medical device.

23. The method ofclaim 13, wherein the medical device is an implantable medical device.

24. A communication system comprising:

an implantable medical device including an implant transceiver;

an external unit including an external unit transceiver;

wherein at least one of the transceivers includes a receiver that samples for a communication at times based upon a macro sampling interval and a micro sampling interval, wherein a duration of a series of samples, spaced by the micro sampling interval, is less than the macro sampling interval.

25. The communication system ofclaim 24, wherein the receiver is part of the implant transceiver.

26. The communication system ofclaim 25, wherein the external unit transceiver includes a transmitter capable of transmitting the communication signal including a preamble segment, an attention segment, a frame sync segment, and data; a duration of the preamble segment being at least as long as the macro sampling interval of the receiver; a duration of the attention segment being at least as long as the micro sampling interval; and wherein the data follows the frame sync segment.

27. The communication system ofclaim 24, wherein the receiver is part of the external unit transceiver.

28. The communication system ofclaim 27, wherein the implant transceiver includes a transmitter for transmitting the communication signal including an attention segment, a frame sync segment, and data, a duration of the attention segment being at least as long as the micro sampling interval of the receiver, and wherein the data follows the frame sync segment.

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